Fix semiring tests

[AK2000]

Added semiring operations to automatically assume same semantics as multiplication. This looks to fix the elementwise addition/subtraction as well but does not truly fix them. Requires #65 to be merged so that the new test case that causes elementwise addition to fail is also in this branch. After these fixes, the test results I see are:

Failed Tests (9):
  COMET :: compound_exps/CSR_Dense_chain_mult_matrix.ta
  COMET :: compound_exps/CSR_mult_spTranspose_CSR.ta
  COMET :: compound_exps/spTranspose_CSR_eltwise_CSR.ta
  COMET :: compound_exps/spTranspose_CSR_mult_CSR.ta
  COMET :: kernels/triangleCount_SandiaLL.ta
  COMET :: kernels/triangleCount_SandiaLL_wMasking.ta
  COMET :: ops/eltwise_mult_DCSRxDense_oDCSR.ta
  COMET :: ops/mult_spgemm_CSRxCSR_oCSR_wMasking.ta
  COMET :: opts/opt_dense_transpose.ta


Testing Time: 1.45s

Total Discovered Tests: 136
  Unsupported:  15 (11.03%)
  Passed     : 112 (82.35%)
  Failed     :   9 (6.62%)